In the furnace at the bottom of the fractionating tower, petroleum is heated to 400 deg C.
The oil vaporizes and enters the fractionating tower at the bottom.
The temperature of the fractionating tower is highest at the bottom and the temperature decreases going up the tower.
As the hot vapour rises up the column, they cool and condense into the trays at various heights depending on their boiling points.
Lighter fractions with the lowest boiling points are distilled over at the top of the fractionating column.
Heavier fractions with the highest boiling points are collected at the bottom of the fractionating column.